How to learn how to make WordPress templates well?

Question

themeforest

I want to learn how to create high-quality templates for sale on sites. What do you need to be able to do for this? What lessons to watch, where to read?
About me:
- I am familiar with html5, css3, js, wordpress

Answer 1

Learn - The WordPress Code, and you can take https://underscores.me/ as a basis

Answer 2

Look here .